Summary Richard Glossip, 52, faces lethal injection over the 1997 fatal beating of a motel owner.
WASHINGTON (AFP) - Advocates for a US man whose execution is scheduled for Wednesday -- among them actress Susan Sarandon and billionaire Richard Branson -- are mobilized in a last-ditch effort to obtain a stay.
Richard Glossip, 52, faces lethal injection over the 1997 fatal beating of a motel owner, but has maintained his innocence for nearly 20 years.
He and two other plaintiffs unsuccessfully took their cases before the US Supreme Court, demanding a ban on a controversial drug used in lethal injections.
But the Supreme Court upheld the use of the drug midazolam in June, saying it does not violate the US Constitution.
Oklahoma Governor Mary Fallin, a Republican, would be able to grant a last-minute stay in the case, which many say lacks sufficient evidence for the death penalty.
An online petition requesting Fallin to halt the execution gained substantial steam with some 230,000 signatures.
Glossip, who worked at the motel, was found guilty of recruiting another employee, Justin Sneed, who was just 19 at the time, to carry out the actual murder.
Glossip was convicted based on the testimony of Sneed, who pleaded guilty and was able to negotiate a life sentence, claiming his co-worker had masterminded the plot.
"I firmly believe, as do so many others, that Richard is innocent of the crime that sent him to Oklahoma s death row," said Sister Helen Prejean, a prominent Catholic nun.
She also called on the public to contact Fallin s office and demand a stay.
Celebrities back Glossip
Meanwhile Sarandon, Branson and US TV personality Phil McGraw, or "Dr Phil," threw their weight behind Glossip s cause.
"Looking at the details of the case, there are plenty of reasons to believe that Glossip did not commit the crimes he was accused of," Branson wrote in a blog post.
"Giving him another opportunity to prove his innocence is not being weak on crime, it s being strong on justice."
Glossip s lawyers produced new evidence earlier this week, requesting time be granted for its review, a move that follows their failed attempt earlier this year at the Supreme Court.
A refusal by manufacturers -- mainly European -- to supply the required drugs has led states like Oklahoma to seek out alternatives, including midazolam.
In April 2014, Oklahoma death-row inmate Clayton Lockett, convicted of murder, rape and kidnapping, took an agonizing 43 minutes to die and could be seen writhing in pain during his prolonged execution.
A few months earlier, Ohio inmate Dennis McGuire, who murdered a pregnant woman, took 26 minutes to die, while Arizona death row convict Joseph Wood, convicted of killing his ex-girlfriend and her father, took 117 minutes in July 2014.
Lethal injection executions are expected to take 10 minutes, and in all three cases, the men could be seen gasping for air.
